1. Field of the Invention
The present invention relates to an antenna apparatus for a linearly polarized diversity antenna in an radio frequency identification (RFID) reader, and a method of controlling the antenna apparatus, and more particularly, to an antenna apparatus for a linearly polarized diversity antenna in an RFID reader, wherein the antenna apparatus communicates with the linearly polarized diversity antenna having the most matching polarization direction with a tag antenna in order to reduce a loss of an electric wave caused by a polarization mismatch, and a method of controlling the antenna apparatus.
2. Description of the Related Art
Conventionally, radio frequency identification (RFID) readers must accurately read data signals emitted from antennas of small RFID tags, which are attached to objects, using an ultrahigh frequency (UHF) band so as to apply to all types of fields including automatic distribution management in harbors, hospitals, and pharmaceutical companies, stock clearance and burglarproofing in stores, automatic arrangement of inventory of books in libraries, automatic searches for bags in airports, automatic control of road environments, traffic control, etc. However, an antenna of a small RFID tag is micro-size and thus, necessarily has a low gain. Also, polarization of the antenna is randomly changed according to an arrangement and a state of an attached object. Thus, a portable reader having a limited size requires a linearly polarized diversity antenna having a small size and a high gain to reduce a loss of an electric wave caused by a polarization mismatch, and transmit and receive data with a tag for a far distance.
However, a conventional tag antenna as described above is conventionally a linearly polarized antenna. Thus, a micro-strip antenna having a circularly polarized characteristic is widely used as a fixed/portable reader antenna. The micro-strip antenna has a constant polarization mismatch loss regardless of the arrangement direction of an attached object. Thus, the micro-strip antenna transmits and receives a constant power to recognize all kinds of tags. As a result, a transceiver circuit of the micro-strip antenna has a relatively simple structure. However, a polarization mismatch loss of 6 dB occurs during two-way communications between a tag and a fixed/portable reader. Due to this, a communication distance between the tag and the reader is shortened.